From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: Re: [PATCH v4] kernel: Add support for power-off handler call chain Date: Tue, 28 Oct 2014 14:10:34 -0700 Message-ID: <20141028211034.GA15820@roeck-us.net> References: <1414516266-4965-1-git-send-email-linux@roeck-us.net> <5361222.IVraj5jbi5@diego> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Received: from bh-25.webhostbox.net ([208.91.199.152]:39972 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752905AbaJ1VLT (ORCPT ); Tue, 28 Oct 2014 17:11:19 -0400 Received: from mailnull by bh-25.webhostbox.net with sa-checked (Exim 4.82) (envelope-from ) id 1XjE2w-000gqH-SY for linux-pm@vger.kernel.org; Tue, 28 Oct 2014 21:11:19 +0000 Content-Disposition: inline In-Reply-To: <5361222.IVraj5jbi5@diego> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Heiko =?iso-8859-1?Q?St=FCbner?= Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Alan Cox , Alexander Graf , Andrew Morton , Geert Uytterhoeven , Lee Jones , Len Brown , Pavel Machek , Philippe =?iso-8859-1?Q?R=E9tornaz?= , "Rafael J. Wysocki" , Romain Perier On Tue, Oct 28, 2014 at 09:58:53PM +0100, Heiko St=FCbner wrote: > Am Dienstag, 28. Oktober 2014, 10:11:06 schrieb Guenter Roeck: > > Various drivers implement architecture and/or device specific means= to > > power off the system. For the most part, those drivers set the glo= bal > > variable pm_power_off to point to a function within the driver. > >=20 > > This mechanism has a number of drawbacks. Typically only one schem= e > > to remove power is supported (at least if pm_power_off is used). > > At least in theory there can be multiple means remove power, some o= f > > which may be less desirable. For example, some mechanisms may only > > power off the CPU or the CPU card, while another may power off the > > entire system. Others may really just execute a restart sequence > > or drop into the ROM monitor. Using pm_power_off can also be racy > > if the function pointer is set from a driver built as module, as th= e > > driver may be in the process of being unloaded when pm_power_off is > > called. If there are multiple power-off handlers in the system, rem= oving > > a module with such a handler may inadvertently reset the pointer to > > pm_power_off to NULL, leaving the system with no means to remove po= wer. > >=20 > > Introduce a system power-off handler call chain to solve the descri= bed > > problems. This call chain is expected to be executed from the arch= itecture > > specific machine_power_off() function. Drivers and architeceture c= ode > > providing system power-off functionality are expected to register w= ith > > this call chain. When registering a power-off handler, callers can > > provide a priority to control power-off handler execution sequence > > and thus ensure that the power-off handler with the optimal capabil= ities > > to remove power for a given system is called first. > >=20 > > Cc: Alan Cox > > Cc: Alexander Graf > > Cc: Andrew Morton > > Cc: Geert Uytterhoeven > > cc: Heiko Stuebner > > Cc: Lee Jones > > Cc: Len Brown > > Cc: Pavel Machek > > Cc: Philippe R=E9tornaz > > Cc: Rafael J. Wysocki > > Cc: Romain Perier > > Signed-off-by: Guenter Roeck > > --- >=20 > Similarly to the restart handlers, I really like the concept. >=20 > Acked-by: Heiko Stuebner >=20 Thanks! Guenter